Conventionally, various technologies for detecting an object existing at the periphery of a vehicle such as an automobile have been proposed. For example, disclosed in Japanese Patent Unexamined Publication No. 2004-196239 is a device which detects an object existing at the periphery of a vehicle when the object actually collides with the vehicle and distinguishes the kind of the object. Though such a device may detect an object existing at the periphery of a vehicle, the device is adapted to conduct detection when the object actually collides with the vehicle so that information about the object distinguished is not used to control a device such as protection device which is activated during the vehicle collision. Therefore, the protection device is activated not only a case where the object is a pedestrian as a primary object to be protected but also a case where the object is a thing not a pedestrian such as a vehicle or a fixed object. Accordingly, there may be a problem of increasing the repair cost (maintenance cost) for the protection device after operation.